1. Field of the Invention
The present invention relates generally to power modules, and more specifically, to the use of flexible circuits in a power module for forming connections to power semiconductor devices.
2. Description of the Prior Art
Referring to FIG. 1 there is shown a top view of a portion of a power module 100 according to the prior art. Power module 100 includes a substrate 102. Formed on the top surface of substrate 102, and possibly within and along the bottom surface thereof, are one or more traces/pads made of copper or the like, such as trace 103. Mounted to these traces are a plurality of semiconductor devices including one or more power switching devices, such as device 104. As an example, the power switching devices may be IGBTs.
Switching device 104 may include along a top surface thereof a first power electrode 106 and a control electrode 108. Along the bottom surface of switching device 104 may be a second power electrode that is mounted to trace 103. The first and second power electrodes may be an emitter electrode and a collector electrode and the control electrode may be a gate electrode. Although not shown in FIG. 1, first power electrode 106 may be wire bonded by a plurality of wire bonds to one or more other traces and/or devices of power module 100.
Power module 100 further includes a first I/O (input-output) contact 110 and a second I/O contact 112 associated with switching device 104. As shown in FIG. 1, the first and second I/O contacts may each include a pad 114 integral with a metal solder lug 116. The first and second I/O contacts are electrically connected to an input and an output of switching device 104. For example, a wire bond 118 may connect the gate electrode 108 of switching device 104 to pad 114 of first I/O contact 110, thereby providing an input gate connection for device 104. Similarly, a wire bond 120 may connect the emitter electrode 106 of switching device 104 to pad 114 of second I/O contact 112, thereby providing an output current sense connection for the device. One skilled in the art will recognize that rather than connecting the emitter electrode 106 of switching device 104 to second I/O contact 112 to obtain a current sense connection, the collector electrode may be connected to the second I/O contact. Similarly, one skilled in the art will also recognize that switching device 104 may include a dedicated current sense output connection that may be interfaced to second I/O contact 112.
Power module 100 further includes a first terminal lead 122 and a second terminal lead 124 associated with switching device 104. As shown in FIG. 1, each of the first and second terminal leads may include a metal solder lug 126 integral with a pad 128, which pad provides for external connection/access to power module 100.
As shown in FIG. 1, wire pairs, such as wires 130 and 132, are used to connect the I/O contacts 110 and 112 of device 104 to terminal leads 122 and 124. Here, wire 130 connects I/O contact 110 to terminal lead 122 and wire 132 connects I/O contact 112 to terminal lead 124. As an example, wires 130 and 132 may be soldered to lugs 116 and 126 of the respective I/O contacts and terminal leads. As shown, wires 130 and 132 are typically twisted in order to reduce the effect of inductive coupling between the two wires, as is known in the art.
In general, the first and second terminal leads 122 and 124 of power module 100 provide an external connection through which control signals can be sent to gate electrode 108 of switching device 104 and through which the current of switching device 104 can be sensed. As an example, a gate driver may be operatively connected to pads 126 of terminal leads 122 and 124 to provide gate control signals to switching device 104 and to sense the current of the switching device.
One skilled in the art will recognize that if power module 100 includes additional switching devices, these additional devices may have a similar configuration as switching device 104.
Notably, the use of twisted wires in power modules like module 100 have several drawbacks. In particular, each wire is typically manually soldered between corresponding pairs of lugs 116 and 126. This manual soldering can be difficult to perform and can lead to long process times in manufacturing a module, thereby affecting cost. In addition, the use of wires in general can lead to variations in wire length between modules and thereby variations in gate loop between modules. Again, controlling such variations leads to increased process control, which can also affect cost.